Liquid crystal display device

ABSTRACT

An operation of floating charged particles and an operation of dispersing charged particles in a liquid crystal layer are controlled by determining strengths of electric fields to be applied to a liquid crystal element in accordance with a state of irradiation of light from a light source of a liquid crystal display device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display devices, andparticularly relates to a liquid crystal display device employing aliquid crystal modulation element.

2. Description of the Related Art

In general, liquid crystal projectors and liquid crystal displays areknown as examples of a liquid crystal display device employing a liquidcrystal element. Such liquid crystal elements employed in liquid crystaldisplay devices include TN (twisted nematic) liquid crystal elementsserving as transmissive liquid crystal elements or VAN (verticalalignment nematic) liquid crystal elements serving as reflection liquidcrystal elements.

Such a liquid crystal element is configured such that liquid crystalfills a portion between a first transparent substrate having atransparent electrode (common electrode) and a second transparentsubstrate having transparent electrodes (pixel electrodes), lines, andswitching elements, for example, which constitute pixels. The portionincluding the liquid crystal is particularly referred to as a liquidcrystal layer.

The liquid crystal element is used to form an image by controlling apolarization state of light which is transmitted through the liquidcrystal. This is carried out by making use of a characteristic in whichan electric field is generated in the liquid crystal layer bycontrolling voltages between electrodes of the liquid crystal element sothat an alignment direction of liquid crystal molecules is changed andthe polarization state of the light transmitted through the liquidcrystal is changed.

However, charged particles are included in the liquid crystal layer andan outer-wall member surrounding the liquid crystal layer, for example.When the liquid crystal is driven in a high-temperature environment, inparticular, the charged particles drift (move). The charged particlesserving as direct-current electric-field components in the liquidcrystal layer are attached to an alignment layer or an electrodeinterface of a liquid crystal layer interface, and the charged particlesdrift and are deposited along the alignment direction of the liquidcrystal molecules.

Furthermore, in liquid crystal elements having organic alignment layers,when the liquid crystal is driven in a high-temperature environment, inaddition to drift of charged particles, charged particles are newlygenerated since organic members such as an alignment layer, liquidcrystal, and a seal member are broken down due to light which isincident onto the liquid crystal elements. These charged particles alsoserve as direct-current electric-field components in a liquid crystallayer, are attached to an alignment layer or an electrode interface of aliquid crystal layer interface, and the charged particles drift and aredeposited along the alignment direction of the liquid crystal molecules.

If an effective electric field to be applied to the liquid crystal ischanged due to the charged particles deposited in a certain region ofthe liquid crystal layer, the polarization state cannot be controlled asdesired and quality of the image is degraded.

Measures to address such a problem have been proposed.

For example, a method for separating ion which causes a stickingphenomenon from an alignment layer or an electrode interface by makingat least one of a potential of a pixel electrode and a potential of acounter electrode of a liquid crystal cell be a ground level while animage display operation is not performed has been proposed (refer toJapanese Patent Laid-Open No. 2005-55562, for example). Furthermore, amethod for arranging a region of ion-trap electrodes in a non-displayregion of a liquid crystal element, and applying a direct currentvoltage to the ion-trap electrodes, so that impurity ion in the regionof the ion-trap electrodes included in the non-display region which isnot used for image display is absorbed has been proposed (refer toJapanese Patent Laid-Open No. 8-201830, for example).

However, when the method disclosed in Japanese Patent Laid-Open No.2005-55562 is used, switching portions used to bring the counterelectrode to the ground level should be included in circuits of theliquid crystal element. Therefore, the number of steps of manufacturingof the liquid crystal elements is increased. Furthermore, when thecounter electrode is merely brought to the ground level, a force forseparating the ion being attached to the alignment layer and theelectrode interface is smaller than the coulomb force, and therefore,only small effect is attained.

Furthermore, when the method disclosed in Japanese Patent Laid-Open No.8-201830 is employed, since the ion-trap electrodes which suck the ionis newly arranged on the non-display region, the number of steps ofmanufacturing the liquid crystal element is increased. In addition,since impurity of the ion is absorbed by the coulomb force and thecoulomb force is in inversed proportion to the squared of a distance,the ion generated in portions separated from the ion-trap electrodescannot be effectively absorbed.

SUMMARY OF THE INVENTION

The present invention provides a liquid crystal display device in whichan adverse effect which is caused by deposition of charged particles ona liquid crystal layer can be avoided without newly adding aconfiguration including switching portions and ion-trap electrodes to aliquid crystal element.

According to an exemplary embodiment of the present invention, there isprovided a liquid crystal display device including a liquid crystalelement configured such that a portion between a first electrode layerand a second electrode layer is filled with liquid crystal, a liquidcrystal driving unit configured to control voltages to be applied to thefirst electrode layer and the second electrode layer so that the liquidcrystal element operates in a first mode in which hourly-averagedstrengths of electric fields to be applied to the liquid crystal at aplurality of portions in an image forming surface of the liquid crystalelement are substantially equal to one another, and thereafter, in asecond mode in which hourly-averaged strengths of electric fields to beapplied to the liquid crystal at a plurality of portions in the imageforming surface of the liquid crystal element are different from oneanother, an irradiating unit configured to irradiate light to the liquidcrystal element, and a controller configured to determine strengths ofthe electric fields to be applied to the liquid crystal layer in thefirst mode or the second mode in accordance with a state of irradiationof light from the irradiating unit.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a projector according to anexemplary embodiment of the present invention.

FIG. 2 is a sectional view illustrating a liquid crystal element.

FIG. 3 is a diagram illustrating a display surface of the liquid crystalelement viewed from a pretilt direction.

FIG. 4 is a diagram illustrating voltages to be applied to a transparentelectrode layer and a reflection pixel electrode layer.

FIG. 5 is a diagram illustrating a state in which charged particles aredeposited on the liquid crystal element.

FIG. 6 is another diagram illustrating the state in which the chargedparticles are deposited on the liquid crystal element.

FIG. 7 is a diagram illustrating a state in which the charged particlesare floated in the liquid crystal layer.

FIG. 8 is a diagram illustrating voltages to be applied to thetransparent electrode layer and the reflection pixel electrode layer.

FIG. 9 is a diagram illustrating distribution of voltages to be appliedto the reflection pixel electrode layer.

FIG. 10 is a diagram illustrating voltages to be applied to thereflection pixel electrode layer for individual display portions of theliquid crystal element.

FIGS. 11A and 11B show a flowchart illustrating control of a floatingoperation and a dispersing operation.

FIG. 12 is a diagram illustrating an example of a pattern imagegenerated in the liquid crystal element.

FIG. 13 is a diagram illustrating another example of the pattern imagegenerated in the liquid crystal element.

FIG. 14 is a diagram illustrating still another example of the patternimage generated in the liquid crystal element.

FIG. 15 is a diagram illustrating a further example of the pattern imagegenerated in the liquid crystal element.

FIG. 16 is a flowchart illustrating control of a floating operation anda dispersing operation.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention will now be described indetail hereinafter with reference to the accompanying drawings.

First Exemplary Embodiment

A projector serving as a liquid crystal display device including aliquid crystal element will be described.

FIG. 1 is a block diagram illustrating main components of the projectoraccording to a first exemplary embodiment of the present invention.

A controller 101 controls blocks of the projector. A data bus 102 isused to transmit and receive various signals such as control signals andimage signals. An operation unit 103 accepts user's operations. A powersupply unit 104 controls electric power supplied to the blocks in theprojector.

An input unit 105 receives image signals transmitted from PCs (PersonalComputers), DVD (Digital Versatile Disc) players, television tuners, andmemory cards, for example. An image processor 106 converts the number ofpixels of an image signal into the appropriate number of pixels inaccordance with the number of pixels of an liquid crystal panel, whichwill be described hereinafter, increases the number of frames of theinput signal for an AC (Alternating Current) driving of the liquidcrystal element, which will be described hereinafter, and performscorrection processing suitable for image formation performed by theliquid crystal element. The correction processing performed by the imageprocessor 106 includes processing of correcting a gamma characteristicof an input image and processing of cancelling uneven brightnessgenerated by an optical system.

A liquid crystal driving unit 107 forms an image in the liquid crystalelement included in a liquid crystal unit 108 in accordance with theimage signal subjected to the correction processing performed by theimage processor 106. When a projector employing three liquid crystalelements is used, for example, the liquid crystal elements arecontrolled for individual three colors so that images for individualthree colors are formed in the corresponding liquid crystal elements. Inthis case, a light beam which is emitted from a light source 109, whichwill be described hereinafter, is separated into three light beamshaving respective three colors, and the three light beams are suppliedto the liquid crystal elements so that the colors of the three lightbeams correspond to the colors of the liquid crystal elements.Thereafter, optical images for individual colors are formed, the opticalimages are combined with one another so that a combined image isobtained, and the combined image is supplied to a projection opticalsystem 111. In this exemplary embodiment, the liquid crystal element isin a vertical alignment nematic (VAN) mode, and liquid crystal moleculesof a liquid crystal layer are aligned substantially perpendicular to anelectrode layer.

The light source 109 emits light to be used to project an image on ascreen (not shown). A light source controller 110 controls an on/offoperation and light quantity of the light source 109. The projectionoptical system 111 is used to project an optical image obtained throughthe liquid crystal unit 108 on the screen (not shown). An optical systemcontroller 112 controls a zooming operation and a focusing operation ofthe projection optical system 111.

A temperature detector 113 disposed near the light source 109 measures atemperature of the light source 109 (performs temperature measurement)and transmits a result of the measurement to the controller 101. A timer114 which works on a battery (not shown) performs time-measurementoperation and transmits a result of the time-measurement operation tothe controller 101. A light sensor 115 measures light which has reachedthe projection optical system 111 (performs a photometry operation), andtransmits a result of the photometry operation to the controller 101.

The controller 101 controls the power supply unit 104, the liquidcrystal driving unit 107, and the light source 109, for example, usingat least one of data items transmitted from the temperature detector113, the timer 114, and the light sensor 115.

Normal operation of the projector will now be described.

The controller 101 included in the projector of this exemplaryembodiment instructs the power supply unit 104 to supply electric powerto the blocks when the operation unit 103 issued an instructionrepresenting power-on. In accordance with the instruction issued by thecontroller 101, the blocks are brought to waiting states. After theelectric power is supplied, the controller 101 instructs the lightsource controller 110 to start light emission from the light source 109.Then, the controller 101 instructs the optical system controller 112 tocontrol the projection optical system 111. The optical system controller112 obtains information on a distance to the screen (not shown), andcontrols the zooming operation and the focusing operation of theprojection optical system 111. Note that the optical system controller112 may control the projection optical system 111 in accordance with anoperation of a user using the operation unit 103.

A projection operation is thus prepared. Then, an image signal inputthrough the input unit 105 is converted into an image signal having aresolution suitable for the liquid crystal unit 108 by the imageprocessor 106, and subjected to the gamma correction and the correctionfor uneven brightness. Then, an image is formed in the liquid crystalunit 108 under the control of the liquid crystal driving unit 107 inaccordance with the image signal which has been subjected to thecorrection performed by the image processor 106.

In general, the liquid crystal element which has received the imagesignal employs a line-inversion driving method in which positivepolarities and negative polarities of electric fields to be applied areinverted for individual lines of aligned pixels, and the positivepolarities and the negative polarities are inverted in a predeterminedperiod such as 60 Hz. Alternatively, a field-inversion driving method inwhich positive polarities and negative polarities of electric fields tobe applied to all aligned pixels are inverted in a predetermined periodmay be employed. Either of the methods may be employed as long as acharacteristic in which even when polarities of electric fields to beapplied to liquid crystal are inverted, a polarization state of lightcan be changed by changing an alignment direction of the molecules.

An example of a configuration of the liquid crystal element of theliquid crystal unit 108 will be described with reference to FIGS. 2 and3. In this exemplary embodiment, the liquid crystal element employed inthe reflection liquid crystal projector will be described.

FIG. 2 is a sectional view illustrating a portion of the liquid crystalelement.

As shown in FIG. 2, the liquid crystal element includes an AR coatinglayer 201, a glass substrate 202, and a transparent electrode layer 203(first electrode layer) which is formed of a transparent electrodearranged on the glass substrate 202. The liquid crystal element furtherincludes a first alignment layer 204 arranged between the transparentelectrode layer 203 and a liquid crystal layer 205.

The liquid crystal element further includes the liquid crystal layer 205arranged between the first alignment layer 204 and a second alignmentlayer 206 which is also included in the liquid crystal element. Theliquid crystal element further includes a reflection pixel electrodelayer 207 (second electrode layer) which is formed of metal such asaluminum and which faces the transparent electrode layer 203, andincludes an Si substrate 208 in which the reflection pixel electrodelayer 207 is arranged thereon. Note that the transparent electrode layer203 and the reflection pixel electrode layer 207 are collectivelyreferred to as an electrode layer as needed hereinafter.

FIG. 3 is a diagram illustrating the liquid crystal element viewed fromthe glass substrate 202.

In FIG. 3, a reference numeral 301 denotes a director direction (pretiltdirection) of liquid crystal molecules aligned by the first alignmentlayer 204, a reference numeral 302 denotes a director direction (pretiltdirection) of the liquid crystal molecules aligned by the secondalignment layer 206, and a reference numeral 303 denotes aliquid-crystal effective display region of an image forming surface. Inthe liquid crystal element, the liquid crystal molecules arranged on thealignment layer are tilted by several degrees so that the liquid crystalmolecules are tilted in a predetermined direction when an electric fieldis applied to the liquid crystal. This tilted direction is referred toas a director direction. Axes of the director directions 301 and 302 aretilted by several degrees in a direction perpendicular to surfaces ofthe alignment layers 204 and 206, are opposite to each other, and aresubjected to alignment processing in a direction tilted by 45 degreesrelative to a short side 303 a and a long side 303 b of the effectivedisplay region 303.

In a normal operation, the liquid crystal driving unit 107 controls avoltage to be applied to the transparent electrode layer 203 to beconstant (for example, 7V) and controls a voltage to be applied to thereflection pixel electrode layer 207 to have a AC waveform so that animage is formed on the liquid crystal element. In this way, an ACelectric field is generated between the transparent electrode layer 203and the reflection pixel electrode layer 207. Note that another methodfor generating an AC electric field may be employed.

FIG. 4 is a diagram illustrating voltages to be applied to thetransparent electrode layer 203 and the reflection pixel electrode layer207.

In FIG. 4, a voltage 401 is to be applied to the transparent electrodelayer 203 and a voltage 402 is to be applied to the reflection pixelelectrode layer 207. The voltage 402 to be applied to the reflectionpixel electrode layer 207 is an AC voltage having a center voltage of7V, an amplitude of 7V, and a frequency of 60 Hz. In general, a degreeof a change of a polarization state of light relies on an absolute valueof a potential difference between the transparent electrode layer 203and the reflection pixel electrode layer 207 irrespective of a polarityof the potential difference. Therefore, in order to prevent flicker frombeing generated, the center voltage of the voltage 402 is substantiallythe same as the voltage 401.

Here, a state of the liquid crystal element obtained when the projectorof this exemplary embodiment has been used for a long period of timewill be described.

Due to light which has high brightness and which is irradiated to thepower supply unit 104 from the light source 109, the power supply unit104 has high temperature for a long period of time. In this state, whenthe liquid crystal molecules are driven, charged particles move in thedirector (pretilt) direction of the liquid crystal molecules along aninterface of the second alignment layer 206 on the reflection pixelelectrode layer 207 side. These charged particles are included in theliquid crystal layer 205, a sealing member which is an organic substancearranged near the liquid crystal layer 205, the alignment layers 204 and206, the transparent electrode layer 203, and the reflection pixelelectrode layer 207, for example. The charged particles move when theliquid crystal display molecules are driven at high temperature.

The charged particles have a characteristic in which the chargedparticles move in a direction in which the liquid crystal molecules ofthe liquid crystal included in the image formation surface of the liquidcrystal element are tilted (that is, an alignment direction).

After moving, the charged particles are deposited in a portion, such asa corner of the effective display region, which relies on the alignmentdirection, in the liquid crystal layer 205. FIGS. 5 and 6 are diagramsillustrating a state in which the charged particles are deposited.

FIG. 5 is a sectional view illustrating a configuration of a portion ofthe liquid crystal element. In FIG. 5, a reference numeral 501 denotesthe charged particles. FIG. 6 is a diagram illustrating the liquidcrystal element viewed from the glass substrate 202 side. In FIG. 6also, the reference numeral 501 denotes the charged particles.

In a case where the charged particles are deposited as shown in FIGS. 5and 6, even when a predetermined voltage is applied between theelectrodes, strength of electric fields to be applied to the liquidcrystal layer is reduced or increased due to electric charge of thecharged particles, and therefore, the electric fields substantiallyapplied to the liquid crystal layer are reduced or increased. In thiscase, substantial strengths of the electric fields to be applied to theliquid crystal are changed due to the charged particles deposited in acertain portion of the liquid crystal layer, and the polarization statecannot be controlled as desired. Accordingly, there arises a problem inthat image quality is degraded.

In order to avoid the state in which the charged particles 501 aredeposited as described above, the charged particles 501 deposited in thecertain portion in the liquid crystal layer are first separated from theelectrode layer, and then, dispersed in the entire liquid crystal layer.Specifically, when negatively-charged particles are deposited, electricfields are applied from the electrode layer in which the chargedparticles are deposited to the other electrode layer so that the chargedparticles float. Then, the charged particles are dispersed in the entireliquid crystal layer by applying, to portions including a large numberof the charged particles, voltages lower than voltages to be applied toother portions.

Here, in this exemplary embodiment, the liquid crystal driving unit 107drives the liquid crystal element of the liquid crystal unit 108 asdescribed below.

In this case, instead of a method for driving the liquid crystal elementby changing a polarity in a predetermined cycle by inverting positiveand negative polarities of the electric fields to be applied to theliquid crystal layer, a method for driving the liquid crystal element inwhich the polarities of the electric fields to be applied to the liquidcrystal layer are not changed (for example, a DC (direct current)electric field is applied to the liquid crystal layer) is used.

In order to float the charged particles 501 which have been deposited inthe state as shown in FIG. 5, the liquid crystal driving unit 107controls voltages so that positive voltages are applied to thetransparent electrode layer 203 of the liquid crystal element andnegative voltages are applied to the reflection pixel electrode layer207 of the liquid crystal element. Then, the controller 101 controls theliquid crystal driving unit 107 so that the voltages are applied for apredetermined period of time. By this, the negatively-charged particles501 deposited on the reflection pixel electrode layer 207 repel thenegative voltages applied to the reflection pixel electrode layer 207,and therefore, the charged particles 501 float as shown in FIG. 7. FIG.8 shows states of the voltages to be applied to the transparentelectrode layer 203 and the reflection pixel electrode layer 207 underthis condition.

In FIG. 8, a reference numeral 801 denotes a voltage to be applied tothe transparent electrode layer 203, and a reference numeral 802 denotesa voltage to be applied to the reflection pixel electrode layer 207.

A polarity of the voltage to be applied to the reflection pixelelectrode layer 207 is not specified as long as the voltage is lowerthan the voltage to be applied to the transparent electrode layer 203.That is, any voltage may be applied as long as a polarity of theelectric field to be applied to the liquid crystal layer 205 issubstantially not changed.

Furthermore, in a plurality of portions in the image forming surface ofthe liquid crystal element, hourly-averaged strengths of electric fieldsto be applied to the liquid crystal layer 205 are substantially thesame.

In this exemplary embodiment, if an electric field is applied from thetransparent electrode layer 203 to the reflection pixel electrode layer207 in an hourly average, the voltage to be applied to the reflectionpixel electrode layer 207 may temporarily exceed the voltage to beapplied to the transparent electrode layer 203.

In a driving mode (first mode) in which an electric field is thusapplied, the charged particles 501 in the liquid crystal layer 205 canbe floated.

An operation of dispersing the floated charged particles 501 will now bedescribed.

In order to disperse the floated charged particles 501, the liquidcrystal driving unit 107 applies voltages to the electrode layer so thatthe charged particles 501 are attracted to a corner which is diagonallyacross from the corner where the floated charged particles 501 have beendeposited. Therefore, for example, different voltages are applied to thereflection pixel electrode layer 207 for individual display portions ofthe liquid crystal element, and the voltages are applied for apredetermined period of time. In this way, the charged particles 501 aremoved by the coulomb force.

In a case where constant voltages of certain levels are to be applied tothe reflection pixel electrode layer 207 while voltages of approximately7V are constantly applied to the transparent electrode layer 203 will bedescribed. FIG. 9 is a diagram illustrating distribution of voltagesapplied to the reflection pixel electrode layer 207.

In FIG. 9, portions in which high voltages are applied to the reflectionpixel electrode layer 207 are shown in white whereas portions in whichlow voltages are applied to the reflection pixel electrode layer 207 areshown in dark color. In FIG. 9, portions 901 and 902 have large amountsof charged particles 501 whereas portions 903 and 904 have small amountsof charged particles 501. Therefore, when the charged particles 501 havenegative polarities, positive voltages are applied to the portions 903and 904 of the reflection pixel electrode layer 207 so that the chargedparticles 501 are attracted.

In FIG. 9, a low voltage is applied to a portion 905, a high voltage isapplied to a portion 907, and a voltage applied to a portion 906 islarger than the voltage applied to the portion 905 but smaller than thevoltage applied to the portion 907.

In this exemplary embodiment, the description is made assuming thatconstant voltages of certain levels are to be applied to the reflectionpixel electrode layer 207. However, the voltages may be irregularlyvaried or the voltages may be AC voltages. That is, any voltage may beapplied as long as a value of integral of a strength of an electricfield to be applied to the liquid crystal at the portion 905 is smallerthan a value of integral of a strength of an electric field applied tothe liquid crystal at the portion 906 and a value of integral of astrength of an electric field applied to the liquid crystal at theportion 907, and the value of integral of the strength of the electricfield to be applied to the liquid crystal at the portion 907 is largerthan the value of integral of the strength of the electric field appliedto the liquid crystal at the portion 905 and the value of integral ofthe strength of the electric field applied to the liquid crystal at theportion 906. FIG. 10 shows voltages to be applied to the reflectionpixel electrode layer 207 at the portions 905 to 907. In this exemplaryembodiment, a case where constant voltages of certain levels are appliedto the reflection pixel electrode layer 207 will be described.

FIG. 10 is a diagram illustrating the voltages to be applied to thereflection pixel electrode layer 207 for individual display portions ofthe liquid crystal element. In FIG. 10, a reference numeral 1001 denotesa voltage applied to the reflection pixel electrode layer 207 at theportion 907, a reference numeral 1002 denotes a voltage applied to thereflection pixel electrode layer 207 at the portion 906, and a referencenumeral 1003 denotes a voltage applied to the reflection pixel electrodelayer 207 at the portion 905.

It is assumed that the liquid crystal element of this exemplaryembodiment does not allow light beams to be transmitted when voltages of7 V are applied to the transparent electrode layer 203 and voltages of 7V are applied to the reflection pixel electrode layer 207 (that is, anegligible amount of electric fields are generated). Furthermore, it isassumed that the liquid crystal element allows most of the light beamsirradiated in the polarization direction to be transmitted when voltagesof 14 V are applied to the reflection pixel electrode layer 207. In thiscase, an image having a pattern shown in FIG. 9 is formed on the liquidcrystal element.

When a voltage of 0V is applied to the liquid crystal element at theportion 905, the liquid crystal element is brought to a bright statesince the liquid crystal element allows most of the light beamsirradiated in the polarization direction. Accordingly, an image having apattern in which the portion 905 becomes bright, the portion 906 becomesdark, and the portion 907 becomes bright may be formed.

When a voltage of 7V is applied to the reflection pixel electrode layer207 at the portion 907, the liquid crystal element is brought to a darkstate since the liquid crystal element prevents the light beams frombeing transmitted. Accordingly, an image having a pattern in which theportion 905 becomes bright, the portion 906 becomes slightly bright, andthe portion 907 becomes dark may be formed.

Furthermore, for the plurality of individual portions in the imageforming surface of the liquid crystal element, hourly-averaged strengthsof electric fields applied to the liquid crystal should be differentfrom one another. In a driving mode (second mode) in which electricfields are thus applied, the charged particles 501 in the liquid crystallayer 205 can be dispersed.

By applying such voltages to the reflection pixel electrode layer 207,the electric field to be applied to the liquid crystal layer 205 can becontrolled so that the negatively-charged particles 501 are floated anddispersed. Accordingly, the quality of an image is prevented from beingdegraded.

In this exemplary embodiment, the description is made assuming that thenegatively-charged particles 501 are used. However, positively-chargedparticles may be deposited on the transparent electrode layer 203. Evenwhen the positively charged particles are deposited, the chargedparticles can be floated and dispersed by performing an operationsimilar to the operation of this exemplary embodiment while polaritiesare changed.

Next, in the operation of the projector described above, control of anoperation of floating the charged particles 501 and an operation ofdispersing the charged particles 501 will be described with reference toFIG. 1 and FIGS. 11 to 15. In this exemplary embodiment, in order toreduce a possibility that an unnecessary pattern image which is formedon the liquid crystal element due to the operation of floating and theoperation of dispersion is recognized by a user, the operations arecontrolled in accordance with a state of the light source 109. In thisexemplary embodiment, the operation of floating the charged particles501 of the liquid crystal element is referred to as a “floatingoperation”, and the operation of dispersing the charged particles 501 isreferred to as a “dispersing operation”. In this exemplary embodiment,the negatively-charged particles 501 are used.

FIGS. 11A and 11B show a flowchart illustrating the control of thefloating operation and the dispersing operation of the projector of thisexemplary embodiment.

First, the controller 101 instructs the power supply unit 104 to supplyelectric power to the blocks of the projector in accordance with aninstruction on power-on issued by the operation unit 103. Then, thecontroller 101 reads, from the timer 114, a time ta which represents aperiod of time from when the power supply was stopped immediately beforea current time to the current time in step S1101.

In step S1102, the controller 101 determines whether the read time ta isequal to or larger than a time t1 representing a period of time theprojector has been stopped (approximately five minutes, for example).

When the determination is affirmative in step S1102, since a long periodof time has been passed after the projector is turned off and before theprojector is turned on again, a certain period of time is requiredbefore the light source 109 becomes totally bright after the projectoris turned on. On the other hand, when the determination is negative instep S1102, since only a short period of time has been passed after theprojector is turned off and before the projector is turned on again, thelight source 109 becomes totally bright within a short period of timeafter the projector is turned on.

In this exemplary embodiment, a state of the light source 109 ispresumed in accordance with a time obtained from the timer 114 so thatelectric fields to be applied to the liquid crystal layer 205 of theliquid crystal element in the floating operation and the dispersingoperation are controlled.

When the determination is affirmative in step S1102, the controller 101resets the timer 114 first, and measures a period of time from when thepower is turned on to a current time, in step S1103. Then, beforeinstructing the liquid crystal driving unit 107 to perform the floatingoperation, the controller 101 instructs the liquid crystal driving unit107 to set V1 (4V, for example) as an upper limit value of a potentialdifference (potential difference between the transparent electrode layer203 and the reflection pixel electrode layer 207) to be applied to theliquid crystal layer 205, in step S1104. When 4V is set as the upperlimit value of the potential difference to be applied to the liquidcrystal layer 205, assuming that constant voltages of 7 V are applied tothe transparent electrode layer 203, the liquid crystal driving unit 107can control the voltages to be applied to the reflection pixel electrodelayer 207 in a range from 3 V to 11 V.

When a value V1 is determined to be the upper limit value of thepotential difference to be applied to the liquid crystal layer 205, theupper limit value can be controlled by setting the upper limit value toa DA converter of the liquid crystal driving unit 107. Alternatively,the upper limit value of the potential difference to be applied to theliquid crystal layer 205 may be controlled by changing a correctionsetting of a gamma correction unit of the liquid crystal driving unit107. These facts are true to throughout the exemplary embodiment.

In step S1105, the controller 101 instructs the liquid crystal drivingunit 107 to perform the floating operation.

When receiving the instruction on the floating operation from thecontroller 101, the liquid crystal driving unit 107 controls thevoltages to be applied to the transparent electrode layer 203 and thevoltages to be applied to the reflection pixel electrode layer 207 so asto control electric fields to be applied to the liquid crystal layer 205of the liquid crystal element. Here, since the charged particles 501 aredeposited on the reflection pixel electrode layer 207, voltages of 7 Vare to be applied to the transparent electrode layer 203 and voltages of3 V are to be applied to the reflection pixel electrode layer 207 sothat a potential difference to be applied to the liquid crystal layer205 corresponds to the value V1 (4 V in this exemplary embodiment) setin advance.

Then, the controller 101 successively receives information blocksregarding time periods which are measured using the timer 114, anddetermines whether a time t which represents a period of time from whenthe power is turned on to a current time is equal to or larger than afloating operation time At2 representing a period of time from when thepower is turned on to a certain time in the floating operation (eightseconds after the power is turned on), in step S1106. When thedetermination is affirmative in step S1106, the controller 101 instructsthe liquid crystal driving unit 107 to set V2 (4 V, for example) as theupper limit value of the potential difference to be applied to theliquid crystal layer 205 when the liquid crystal driving unit 107performs the dispersing operation, in step S1107.

Thereafter, in step S1108, the controller 101 instructs the liquidcrystal driving unit 107 to perform the dispersing operation.

When receiving the instruction on the dispersing operation, the liquidcrystal driving unit 107 controls the voltages to be applied to thetransparent electrode layer 203 and the voltages to be applied to thereflection pixel electrode layer 207 so as to control the electric fieldto be applied to the liquid crystal layer 205 of the liquid crystalelement. Here, voltages of 7 V, for example, are to be applied to thetransparent electrode layer 203. In this case, since the chargedparticles 501 are negatively charged, voltages of 11 V are to be appliedto portions in which the charged particles 501 on the reflection pixelelectrode layer 207 are to be attracted whereas voltages of 7 V are tobe applied to portions in which the charged particles 501 are to bemoved away. This operation is performed so that the voltages to beapplied to the portions in which the charged particles 501 are to beattracted and which generate a larger potential difference become largerthan the voltages to be applied to the transparent electrode layer 203by the value V2 in order to attain a potential difference to be appliedto the liquid crystal layer 205 corresponding to the value V2 (4 V inthis exemplary embodiment) set in advance.

FIG. 12 is a diagram illustrating an example of a pattern imagegenerated on the liquid crystal element when the value V2 is set as theupper limit value of the potential difference to be applied to theliquid crystal layer 205.

Alternatively, voltages of 11 V may be applied to the portions in whichthe charged particles 501 on the reflection pixel electrode layer 207are to be attracted and voltages of 3 V may be applied to the portionsin which the charged particles 501 are moved away. Furthermore, voltagesof 7 V may be applied to the portions in which the charged particles 501on the reflection pixel electrode layer 207 are to be attracted andvoltages of 3 V may be applied to the portions in which the chargedparticles 501 are moved away. When the voltages to be applied to thereflection pixel electrode layer 207 are changed, a pattern imagedifferent from the pattern image shown in FIG. 12 is obtained. However,brightness at portions having the highest brightness is substantiallythe same as that shown in FIG. 12.

In step S1109, the controller 101 successively receives informationblocks regarding time periods which are measured using the timer 114,and determines whether the time t which represents a period of time fromwhen the power is turned on to a current time is equal to or larger thana dispersing operation time At3 representing a period of time from whenthe power is turned on to a certain time in the dispersing operation (12seconds after the power is turned on).

When the determination is affirmative in step S1109, the controller 101instructs the liquid crystal driving unit 107 to set a value V3 (3 V,for example) as the upper limit value of the potential difference to beapplied to the liquid crystal layer 205 when the liquid crystal drivingunit 107 performs the dispersing operation, in step S1110.

Here, the light source 109 gradually becomes bright after the dispersingoperation time At3 (12 seconds, for example) has passed after the poweris turned on. Furthermore, in the liquid crystal element of thisexemplary embodiment, the larger the potential difference to be appliedto the liquid crystal layer 205 is, the easier the light beams aretransmitted. Here, when the potential difference to be applied to theliquid crystal layer 205 is approximately the value V2 and when thelight beams transmitted through the liquid crystal are projected on ascreen, a difference between bright and dark may be recognized by theuser.

Therefore, by changing the upper limit value of the potential differenceto be applied to the liquid crystal layer 205 to the value V3 which issmaller than the value V2, the difference between bright and dark isreduced so as to be prevented from being recognized by the user.

After the controller 101 changes the upper limit value of the potentialdifference to be applied to the liquid crystal layer 205 from the valueV2 to the value V3, the liquid crystal driving unit 107 controls thevoltages to be applied to the transparent electrode layer 203 and thevoltages to be applied to the 207. Then, the potentials to be applied tothe portions in which the charged particles 501 on the reflection pixelelectrode layer 207 are to be attracted are changed from 11 V to 10 V.This operation is performed so that the voltages to be applied to theportions in which the charged particles 501 are to be attracted andwhich generate a larger potential difference become larger than thevoltages to be applied to the transparent electrode layer 203 by thevalue V3 in order to attain a potential difference to be applied to theliquid crystal layer 205 corresponding to the value V3 (3 V in thisexemplary embodiment) set in advance.

FIG. 13 is a diagram illustrating an example of a pattern imagegenerated on the liquid crystal element when the value V3 is set as theupper limit value of the potential difference to be applied to theliquid crystal layer 205. Portions having the highest brightness shownin FIG. 13 are darker than the portions having the highest brightnessshown in FIG. 12, and a difference between bright and dark are smallerthan that of FIG. 12.

Alternatively, voltages of 10 V may be applied to the portions in whichthe charged particles 501 on the reflection pixel electrode layer 207are to be attracted and voltages of 4 V may be applied to the portionsin which the charged particles 501 on the reflection pixel electrodelayer 207 are to be moved away. Furthermore, voltages of 7 V may beapplied to the portions in which the charged particles 501 on thereflection pixel electrode layer 207 are attracted, and voltages of 4 Vmay be applied to the portions in which the charged particles 501 are tobe moved away. When the voltages to be applied to the reflection pixelelectrode layer 207 are changed, a pattern image different from thepattern image shown in FIG. 13 is obtained. However, brightness atportions having the highest brightness is substantially the same as thatshown in FIG. 13, and the difference between bright and dark of thepattern image is smaller than that of FIG. 12.

In step S1111, the controller 101 successively receives informationblocks regarding time periods which are measured using the timer 114,and determines whether the time t which represents a period of time fromwhen the power is turned on to a current time is equal to or larger thana dispersing operation time Bt4 representing a period of time from whenthe power is turned on to a certain time in the dispersing operation (16seconds after the power is turned on). When the determination isaffirmative in step S1111, the controller 101 instructs the liquidcrystal driving unit 107 to set a value V4 (2 V, for example) as theupper limit value of the potential difference to be applied to theliquid crystal layer 205 when the liquid crystal driving unit 107performs the dispersing operation, in step S1112.

Here, the light source 109 gradually becomes brighter after thedispersing operation time Bt4 (16 seconds, for example) has passed afterthe power is turned on. Here, when the potential difference to beapplied to the liquid crystal layer 205 is approximately the value V3and when the light beams transmitted through the liquid crystal areprojected on the screen, a difference between bright and dark may berecognized by the user. Therefore, by changing the upper limit value ofthe potential difference to be applied to the liquid crystal layer 205to the value V4 which is smaller than the value V3, the differencebetween bright and dark is reduced so as to be prevented from beingrecognized by the user.

After the controller 101 changes the upper limit value of the potentialdifference to be applied to the liquid crystal layer 205 from the valueV3 to the value V4, the liquid crystal driving unit 107 controls thevoltages to be applied to the transparent electrode layer 203 and thevoltages to be applied to the 207. Then, the potentials to be applied tothe portions in which the charged particles 501 on the reflection pixelelectrode layer 207 are to be attracted are changed from 10 V to 9 V.This operation is performed so that the voltages to be applied to theportions in which the charged particles 501 are to be attracted andwhich generate a larger potential difference become larger than thevoltages to be applied to the transparent electrode layer 203 by thevalue V4 in order to attain a potential difference to be applied to theliquid crystal layer 205 corresponding to the value V4 (2 V in thisexemplary embodiment) set in advance.

FIG. 14 is a diagram illustrating an example of a pattern imagegenerated on the liquid crystal element when the value V4 is set as theupper limit value of the potential difference to be applied to theliquid crystal layer 205. Portions having the highest brightness shownin FIG. 14 are darker than the portions having the highest brightnessshown in FIGS. 12 and 13, and a difference between bright and dark onthe display surface are smaller than those of FIGS. 12 and 13.

Alternatively, voltages of 9 V may be applied to the portions in whichthe charged particles 501 on the reflection pixel electrode layer 207are to be attracted and voltages of 5 V may be applied to the portionsin which the charged particles 501 on the reflection pixel electrodelayer 207 are to be moved away. Furthermore, voltages of 7 V may beapplied to the portions in which the charged particles 501 on thereflection pixel electrode layer 207 are attracted, and voltages of 5 Vmay be applied to the portions in which the charged particles 501 are tobe moved away. When the voltages to be applied to the reflection pixelelectrode layer 207 are changed, a pattern image different from thepattern image shown in FIG. 14 is obtained. However, brightness atportions having the highest brightness is substantially the same as thatshown in FIG. 14, and the difference between bright and dark of thepattern image is smaller than those of FIGS. 12 and 13.

In step S1113, the controller 101 successively receives informationblocks regarding time periods which are measured using the timer 114,and determines whether the time t which represents a period of time fromwhen the power is turned on to a current time is equal to or larger thana dispersing operation time Ct5 representing a period of time from whenthe power is turned on to a certain time in the dispersing operation (22seconds after the power is turned on). When the determination isaffirmative in step S1113, the controller 101 instructs the liquidcrystal driving unit 107 to stop the dispersing operation in step S1114.

After the dispersing operation time Ct5 (22 seconds, for example) haspassed after the power is turned on, it is determined that a period oftime sufficient for the dispersion of the charged particles 501 of theliquid crystal element has passed. Therefore, the dispersing operationis terminated. In step S1115, the controller 101 instructs the liquidcrystal driving unit 107 to normally operate the liquid crystal unit108.

Then, the user can use the projector in the normal usage.

After an image is normally projected, in accordance with an instructionon power-off issued by the operation unit 103 in step S1116, thecontroller 101 instructs the power supply unit 104 to supply power tothe blocks of the projector. Then, the controller 101 resets the timer114 so that a period of time from when the power is turned off ismeasured in step S1117. The operation of the projector is thusterminated.

A case where the read time ta is larger than the stop time t1 (when thedetermination is negative in step S1102) will now be described. In stepS1118, the controller 101 resets the timer 114 and instructs the timer114 to measure a period of time from when the power is turned on to acurrent time. Then, before instructing the liquid crystal driving unit107 to perform the floating operation, the controller 101 instructs theliquid crystal driving unit 107 to set a value V5 (1 V, for example) asthe upper limit value of the potential difference (potential differencebetween the transparent electrode layer 203 and the reflection pixelelectrode layer 207) to be applied to the liquid crystal layer 205, instep S1119.

Note that a potential difference of a degree in which the pattern imageis not recognized by the user even when the light source 109 is totallybright is preferably set as the upper limit value V5. In addition, aperiod of time in which the potential difference is applied ispreferably set to be long since the potential difference is small.

In step S1120, the controller 101 instructs the liquid crystal drivingunit 107 to perform the floating operation.

When receiving the instruction on the floating operation from thecontroller 101, the liquid crystal driving unit 107 controls thevoltages to be applied to the transparent electrode layer 203 and thevoltages to be applied to the reflection pixel electrode layer 207 so asto control electric fields to be applied to the liquid crystal layer 205of the liquid crystal element. Here, since the charged particles 501 aredeposited on the reflection pixel electrode layer 207, voltages of 7 Vare to be applied to the transparent electrode layer 203 and voltages of6 V are to be applied to the reflection pixel electrode layer 207.

Then, the controller 101 successively receives information blocksregarding time periods which are measured using the timer 114, anddetermines whether the time t which represents a period of time fromwhen the power is turned on to a current time is equal to or larger thana floating operation time Bt6 representing a period of time from whenthe power is turned on to a certain time in the floating operation (30seconds after the power is turned on), in step S1121. When thedetermination is affirmative in step S1121, the controller 101 instructsthe liquid crystal driving unit 107 to set a value V6 (1 V, for example)as the upper limit value of the potential difference to be applied tothe liquid crystal layer 205 when the liquid crystal driving unit 107performs the dispersing operation, in step S1122.

Thereafter, in step S1123, the controller 101 instructs the liquidcrystal driving unit 107 to perform the dispersing operation.

When receiving the instruction on the dispersing operation, the liquidcrystal driving unit 107 controls the voltages to be applied to thetransparent electrode layer 203 and the voltages to be applied to thereflection pixel electrode layer 207 so as to control the electric fieldto be applied to the liquid crystal layer 205 of the liquid crystalelement. Here, voltages of 7 V, for example, are to be applied to thetransparent electrode layer 203. In this case, since the chargedparticles 501 are negatively charged, voltages of 8 V are to be appliedto the portions in which the charged particles 501 on the reflectionpixel electrode layer 207 are to be attracted whereas voltages of 7 Vare applied to the portions in which the charged particles 501 are to bemoved away. This operation is performed so that the voltages to beapplied to the portions in which the charged particles 501 are to beattracted and which generate a larger potential difference become largerthan the voltages to be applied to the transparent electrode layer 203by the value V6 in order to attain a potential difference to be appliedto the liquid crystal layer 205 corresponding to the value V6 (1 V inthis exemplary embodiment) set in advance. Here, a potential differenceof a degree in which the pattern image is not recognized by the usereven when the light source 109 is totally bright is preferably set tothe upper limit value V6.

FIG. 15 is a diagram illustrating an example of a pattern imagegenerated on the liquid crystal element when the value V6 is set as theupper limit value of the potential difference to be applied to theliquid crystal layer 205.

Alternatively, voltages of 8 V may be applied to the portions in whichthe charged particles 501 on the reflection pixel electrode layer 207are to be attracted and voltages of 6 V may be applied to the portionsin which the charged particles 501 are moved away. Furthermore, voltagesof 7 V may be applied to the portions in which the charged particles 501on the reflection pixel electrode layer 207 are to be attracted andvoltages of 6 V may be applied to the portions in which the chargedparticles 501 are moved away. When the voltages to be applied to thereflection pixel electrode layer 207 are changed, a pattern imagedifferent from the pattern image shown in FIG. 15 is obtained. However,brightness at portions having the highest brightness is substantiallythe same as that shown in FIG. 15.

In step S1124, the controller 101 successively receives informationblocks regarding time periods which are measured using the timer 114,and determines whether the time t which represents a period of time fromwhen the power is turned on to a current time is equal to or larger thana dispersing operation time Dt7 representing a period of time from whenthe power is turned on to a certain time in the dispersing operation (40seconds after the power is turned on). When the determination isaffirmative in step S1124, the process proceeds to step S1114.

As described above, the projector of this exemplary embodiment presumesthe state of the light source 109 in accordance with the informationblocks obtained using the timer 114, and controls the electric fields tobe applied to the liquid crystal layer 205 in the floating operation andthe dispersing operation. In this way, the projector of this exemplaryembodiment reduces the possibility that a pattern image which is formedon the liquid crystal element due to the floating operation and thedispersing operation is recognized by a user.

In this exemplary embodiment, the state of the light source 109 ispresumed in accordance with the information blocks obtained using thetimer 114. However, the state of the light source 109 may be presumed inaccordance with information blocks representing temperatures of thelight source 109 obtained using the temperature detector 113, and theoperation is performed in accordance with the flowchart of FIGS. 11A and11B.

In this case, in step S1102 of FIG. 11A, the controller 101 determineswhether a temperature T of the light source 109 obtained using thetemperature detector 113 is lower than a stop temperature T1representing a certain temperature of the projector which has beenstopped. In this way, it can be presumed whether the light source 109 ofthe projector can be immediately turned on with full brightness.

Furthermore, in this case, in step S1106 of FIG. 11A, the controller 101determines whether the temperature T of the light source 109 obtainedusing the temperature detector 113 is larger than a floating operationtemperature AT2 representing a certain temperature of the projector inthe floating operation. In this way, a determination as to whether thefloating operation has been performed for a sufficient period of timecan be made.

Similarly, in this case, the controller 101 determines whether thetemperature T of the light source 109 obtained using the temperaturedetector 113 is higher than certain temperatures of step S1109, stepS1111, step S1113, step S1121, and step S1124 in respective step S1109,step S1111, step S1113, step S1121, and step S1124 of FIG. 11A. In thisway, a determination as to whether the state of brightness of the lightsource 109 has reached a predetermined state can be made.

Alternatively, the timer 114 may be used to determine whether thefloating operation and the dispersing operation are sufficientlyperformed.

Furthermore, the operation of the flowchart of FIGS. 11A and 11B may beperformed by presuming the state of the light source 109 in accordancewith information on light quantity of the light source 109 obtainedusing the light sensor 115.

In this case, in step S1102 of FIG. 11A, the controller 101 determineswhether a light quantity P obtained using the light sensor 115 issmaller than a stop light quantity P1 representing a certain lightquantity of the projector which has been stopped. In this way, it can bepresumed whether the light source 109 of the projector can beimmediately turned on with full brightness.

Furthermore, in this case, in step S1106 of FIG. 11A, the controller 101determines whether the light quantity P obtained using the light sensor115 is larger than a floating operation light quantity AP1 representinga certain light quantity in the floating operation. In this way, adetermination as to whether the floating operation is performed for asufficient period of time can be made.

Similarly, in this case, the controller 101 determines whether the lightquantity P obtained using the light sensor 115 is larger than certainlight quantities of step S1109, step S1111, step S1113, step S1121, andstep S1124 of FIG. 11A. In this way, a determination as to whether thestate of brightness of the light source 109 has reached a predeterminedstate can be made.

Alternatively, the timer 114 may be used to determine whether thefloating operation and the dispersing operation are sufficientlyperformed.

Furthermore, the state of the light source 109 may be presumed taking acombination of the information obtained using the temperature detector113, the information obtained using the timer 114, and the informationobtained using the light sensor 115 into consideration.

Moreover, the light sensor 115 may measure light quantity or light flux.

In this exemplary embodiment, the description is made assuming thatconstant voltages of certain levels are to be applied to the transparentelectrode layer 203 and constant voltages of certain levels are to beapplied to the reflection pixel electrode layer 207. However, thevoltages may be irregularly varied or the voltages may be AC voltages.In this exemplary embodiment, the electric fields to be applied to theliquid crystal layer 205 are controlled by controlling the potentialdifference between the transparent electrode layer 203 and thereflection pixel electrode layer 207. Accordingly, the constant voltagesare not necessarily used.

Furthermore, in the liquid crystal element, the charged particles may becombined with charges having polarities opposite to those included inthe liquid crystal when the liquid crystal element is driven. Thecharged particles combined with the charges having the oppositepolarities are brought to neutral states due to the combined charges.Even when the electric fields are applied to such charged particles inorder to perform the floating operation and the dispersing operation,the coulomb force does not work, and therefore, the charged particlesare not floated and not dispersed.

By leaving the liquid crystal element for a long period of time withoutbeing driven, the charged particles in the neutral states return to thecharged particles in an original state after the combinations with thecharges having the opposite polarities are cancelled by themselves. Inthis state, the charged particles have been negatively charged.

In this exemplary embodiment, a determination as to whether the floatingoperation is to be performed and a determination as to whether thedispersing operation is to be performed are made in accordance withstates of the charged particles in the liquid crystal element. By this,the floating operation or the dispersing operation can be performed whenthe charged particles can be effectively floated or dispersed.

Specifically, the controller 101 controls the liquid crystal drivingunit 107 so that the floating operation and the dispersing operation areperformed when the charged particles in the liquid crystal element arenot combined with the charges having the polarities opposite to those inthe liquid crystal whereas the floating operation and the dispersingoperation are not performed when the charged particles are combined withthe charges having the polarities opposite to those in the liquidcrystal.

A method for presuming the state of the charged particles 501 in theliquid crystal element will now be described.

As described above, by leaving the liquid crystal element for a longperiod of time without being driven, the charged particles in theneutral states return to the charged particles in the original stateafter the combinations with the charges having opposite polarities arecancelled by themselves.

Therefore, if a determination as to whether the liquid crystal elementhas not been driven for a long period of time can be made, the state ofthe charged particles included in the liquid crystal element can bepresumed.

In this exemplary embodiment, it is determined whether the liquidcrystal element has not been driven for a long period of time inaccordance with a temperature of the liquid crystal element, atemperature of the light source 109, a period of time from when thepower is turned off to when the power is turned on, and quantity oflight (light flux) emitted from the light source 109.

In a case where it is determined whether the liquid crystal element hasnot been driven for a long period of time in accordance with thetemperature of the liquid crystal element, the temperature detector 113detects the temperature of the liquid crystal element. When thetemperature detected by the temperature detector 113 is higher than apredetermined value, the controller 101 determines that the liquidcrystal element is not in the state in which the liquid crystal elementhas not been driven for a long period of time whereas when thetemperature detected by the temperature detector 113 is lower than thepredetermined value, the controller 101 determines that the liquidcrystal element is in the state in which the liquid crystal element hasnot been driven for a long period of time. In this case, thepredetermined value corresponds to approximately 25° C. or approximately20° C., for example.

In a case where it is determined whether the liquid crystal element hasnot been driven for a long period of time in accordance with thetemperature of the liquid crystal element, the temperature detector 113detects the temperature of the light source 109. When the temperaturedetected by the temperature detector 113 is higher than a predeterminedvalue, the controller 101 determines that the liquid crystal element isnot in the state in which the liquid crystal element has not been drivenfor a long period of time whereas when the temperature detected by thetemperature detector 113 is lower than the predetermined value, thecontroller 101 determines that the liquid crystal element is in thestate in which the liquid crystal element has not been driven for a longperiod of time. In this case, the predetermined value corresponds toapproximately 25° C. or approximately 20° C., for example.

In a case where it is determined whether the liquid crystal element hasnot been driven for a long period of time in accordance with the periodof time from when the power is turned off to when the power is turnedon, the timer 114 detects the period of time. The timer 114 measures theperiod of time from when the power is turned off to when the power isturned on. When information on the period of time measured by the timer114 is larger than a predetermined value, the controller 101 determinesthat the liquid crystal element is in the state in which the liquidcrystal element has not been driven for a long period of time whereaswhen the information of the period of time measured by the timer 114 issmaller than the predetermined value, the controller 101 determines thatthe liquid crystal element is not in the state in which the liquidcrystal element has not been driven for a long period of time. In thiscase, the predetermined value corresponds to approximately 100 hours orapproximately 200 hours, for example.

In a case where it is determined whether the liquid crystal element hasnot been driven for a long period of time in accordance with thequantity of light (light flux) emitted from the light source 109, thelight sensor 115 detects the light quantity or the light flux. When thelight quantity obtained by the light sensor 115 is smaller than apredetermined value, the controller 101 determines that the liquidcrystal element is in the state in which the liquid crystal element hasnot been driven for a long period of time whereas when the lightquantity obtained by the light sensor 115 is larger than thepredetermined value, the controller 101 determines that the liquidcrystal element is not in the state in which the liquid crystal elementhas not been driven for a long period of time.

The determination as to whether the liquid crystal element has not beendriven for a long period of time is made as described above.

The control of the floating operation and the dispersing operationperformed by the projector of this exemplary embodiment will now bedescribed. FIG. 16 is a flowchart illustrating the control of thefloating operation and the dispersing operation.

In step S1601, the controller 101 instructs the power supply unit 104 tosupply the electric power to the blocks in accordance with aninstruction on power-on issued by the operation unit 103.

After the electric power is supplied to the blocks, the controller 101determines whether the liquid crystal element has not been driven for along period of time in step S1602.

When the determination is negative in step S1602, the controller 101instructs the liquid crystal driving unit 107 to normally operate theliquid crystal unit 108 in step S1608.

On the other hand, when the determination is affirmative in step S1602,the controller 101 instructs the liquid crystal driving unit 107 toperform the floating operation in step S1603.

Thereafter, the controller 101 successively receives information blocksregarding periods of times measured by the timer 114, and determineswhether the time t representing the period of time from when the poweris turned on to a current time is equal to or larger than the floatingoperation time At2 in step S1604. When the determination is affirmativein step S1604, the controller 101 instructs the liquid crystal drivingunit 107 to perform the dispersing operation in step S1605.

In step S1606, the controller 101 successively receives informationblocks regarding periods of times measured by the timer 114, anddetermines whether the time t representing the period of time from whenthe power is turned on to a current time is equal to or larger than thedispersing operation time t2 representing a certain time in thedispersing operation (20 seconds after the power is turned on).

When the determination is affirmative in step S1606, the controller 101instructs the liquid crystal driving unit 107 to stop the dispersingoperation in step S1607. Then, the controller 101 instructs the liquidcrystal driving unit 107 to normally operate the liquid crystal unit 108in step S1608.

Then, the user uses the projector in the normal usage.

After a normal image is projected, the controller 101 instructs thepower supply unit 104 to supply the electric power to the blocks of theprojector in accordance with an instruction on power-off issued by theoperation unit 103 in step S1609.

By this, in accordance with the state of the charged particles 501 inthe liquid crystal element, the projector of this exemplary embodimentperforms the floating operation or the dispersing operation when thecharged particles 501 can be effectively floated or dispersed.

In this exemplary embodiment, the determination as to whether the liquidcrystal element has not been driven for a long period of time may bemade taking a combination of information obtained using the temperaturedetector 113, information obtained using the timer 114, and informationobtained using the light sensor 115 into consideration. That is, thestate of the charged particles 501 in the liquid crystal element may bepresumed taking a combination of the information obtained using thetemperature detector 113, the information obtained using the timer 114,and the information obtained using the light sensor 115 intoconsideration.

In this exemplary embodiment, the description is made taking theprojector as an example. However, the present invention is applicable toany display device having such a liquid crystal element, such as aliquid crystal television set, a liquid crystal display device, adigital still camera, a portable game machine, and a cellular phone, forexample.

This exemplary embodiment is applicable to the liquid crystal modulationelement in the vertical alignment nematic (VAN) mode. However, theoperation of controlling the applied voltages may be modified so as tobe suitable for liquid crystal modulation elements of a TN mode, an STN(Super Twist Nematic) mode, and an OCB (Optically CompensatedBirefringence) mode, and may be applied to these liquid crystalmodulation elements. Furthermore, the operation of controlling theapplied voltages may be modified so as to be suitable for transmissiveliquid crystal modulation element.

It is apparent that an object of the present invention is realized bysupplying a storage medium including program code of software whichattains the functions of the exemplary embodiment to a device. In thiscase, a computer (a CPU or a MPU) serving as a controller of the devicewhich received the storage medium reads and executes the program codestored in the storage medium.

In this case, the program code read from the storage medium realizes thefunctions of the exemplary embodiment described above, and therefore,the program code itself and the storage medium including the programcode stored therein are included in the present invention.

Examples of the storage medium used to supply the program code include aflexible disk, a hard disk, an optical disc, a magneto-optical disc, aCD-ROM (Compact Disc Read-Only Memory), a CD-R (Compact Disc Readable),a magnetic tape, a nonvolatile memory card, and a ROM.

It is apparent that a case where an OS (Operating System), i.e., a basicsystem which operates in the device performs part of or entireprocessing, and the functions of the exemplary embodiment are realizedin accordance with the processing is included in the present invention.

Furthermore, it is apparent that a case where the program code read fromthe storage medium is written to a memory included in a functionexpansion board inserted into the device or a memory included in afunction expansion unit connected to the computer so that the functionsof the exemplary embodiment are realized is included in the presentinvention. Here, a CPU included in the function expansion board or a CPUincluded in the function expansion unit performs part of or entireprocessing in accordance with instructions represented by the programcode.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2008-120405 filed May 2, 2008 and No. 2008-121163 filed May 7, 2008,which are hereby incorporated by reference herein in their entirety.

1. A liquid crystal display device comprising: a liquid crystal elementconfigured such that a portion between a first electrode layer and asecond electrode layer is filled with liquid crystal; a liquid crystaldriving unit configured to control voltages to be applied to the firstelectrode layer and the second electrode layer so that the liquidcrystal element operates in a first mode in which time-averagedstrengths of electric fields to be applied to the liquid crystal at aplurality of portions in an image forming surface of the liquid crystalelement are substantially equal to one another, and thereafter, in asecond mode in which time-averaged strengths of electric fields to beapplied to the liquid crystal at a plurality of portions in the imageforming surface of the liquid crystal element are different from oneanother; an irradiating unit configured to irradiate light to the liquidcrystal element; and a controller configured to determine strengths ofthe electric fields to be applied to the liquid crystal layer in thefirst mode or the second mode in accordance with a light quantity outputfrom the irradiating unit.
 2. The liquid crystal display deviceaccording to claim 1, wherein the controller determines a period of timein which the electric fields are applied in the first mode or the secondmode in accordance with the light quantity output from the irradiatingunit.
 3. The liquid crystal device according to claim 1, wherein thecontroller controls the liquid crystal driving unit so that the liquidcrystal element operates in the first mode until charged particlesdeposited on the first electrode layer or the second electrode layerincluded in the liquid crystal layer are floated in the liquid crystallayer, and the controller controls the liquid crystal driving unit sothat the liquid crystal element operates in the second mode until thecharged particles included in the liquid crystal layer move in adirection different from a direction in which liquid crystal moleculesof the liquid crystal in the image forming surface of the liquid crystalelement are tilted.
 4. The liquid crystal display device according toclaim 1, wherein, in the second mode, time-averaged strengths ofelectric fields to be applied to the liquid crystal at a plurality ofportions which is tilted in a direction different from a direction inwhich liquid crystal molecules of the liquid crystal in the imageforming surface of the liquid crystal element are tilted in advance aredifferent from one another.
 5. The liquid crystal display deviceaccording to claim 1, further comprising: a timer configured to measurea time period regarding the irradiating unit, wherein the controllerdetermines the light quantity output from the irradiating unit inaccordance with information obtained by the timer.
 6. The liquid crystaldisplay device according to claim 1, further comprising: a temperaturemeasuring unit configured to measure a temperature regarding theirradiating unit, wherein the controller determines the light quantityoutput from the irradiating unit in accordance with information obtainedby the temperature measuring unit.
 7. The liquid crystal display deviceaccording to claim 1, wherein liquid crystal molecules of the liquidcrystal included in the liquid crystal element are aligned substantiallyperpendicular to the first electrode layer and the second electrodelayer.
 8. A liquid crystal display device comprising: a liquid crystalpanel configured such that a portion between a first electrode layer anda second electrode layer is filled with liquid crystal; a light sourceconfigured to supply light to the liquid crystal panel; and a drivingunit configured to control a voltage to be applied to the liquid crystalof the liquid crystal panel, wherein the driving unit applies thevoltage for dispersing charged particles in the liquid crystal of theliquid crystal panel to the liquid crystal panel, wherein the drivingunit controls strength of the voltage for dispersing the chargedparticles in accordance with light quantity of the light source, andwherein, as the light quantity of the light source becomes larger, thedriving unit lowers the voltage for dispersing the charged particles. 9.The liquid crystal display device according to claim 8, wherein, as avoltage for dispersing the charged particles, the driving unit mutuallydifferentiates time-averaged strength of the voltage to be applied tothe liquid crystal in a plurality of positions of the liquid crystalpanel.
 10. The liquid crystal display device according to claim 8,wherein, after turning on the liquid crystal display device, the drivingunit applies a voltage to float the charged particles in the liquidcrystal before applying a voltage to disperse the charged particles tothe liquid crystal panel.
 11. The liquid crystal display deviceaccording to claim 10, wherein, as a voltage for floating the chargedparticles in the liquid crystal, the driving unit sets time-averagedstrength of a voltage applied to the liquid crystal as nearly equal witheach other in a plurality of positions of the liquid crystal panel. 12.The liquid crystal display device according to claim 8, wherein lightquantity of the light source is estimated based on an output result froma light sensor, a timer and a temperature detector.